The present invention relates generally to medical devices, and more particularly to methods and apparatus for the endoluminal placement of tubular prostheses, such as grafts, for repairing aneurysms or other vascular defects in humans and animals.
Aneurysms are discrete dilations of the arterial wall, caused by weakening of the arterial wall. One of the most common, and among the most life threatening, is an aneurysm of the abdominal aorta between the renal and iliac arteries. If untreated, the aneurysm dilates progressively with an ever increasing risk of rupture and hemorrhagic death.
One method of treatment is provided by direct surgical intervention, in which the defective vessel may be bypassed or replaced using a prosthetic device such as a synthetic graft. The risks involved in direct surgical intervention of this magnitude are great, and include an extensive recovery period.
In recent years a less invasive method of treatment has evolved through a series of inventions. The details vary, but, conventionally, a resilient tubular conduit fashioned from flexible fabric (herein referred to as a xe2x80x9cgraftxe2x80x9d) is introduced into the defective vessel by means of catheters introduced into the femoral artery. The graft is attached to the non-dilated or slightly dilated arteries above and below the aneurysm using expandable metallic cylinders (herein referred to as xe2x80x9cattachment systemsxe2x80x9d) which may include barbs or hooks to enhance attachment to the vascular wall.
When an attachment system is positioned on the interior of a graft""s lumen, it will tend to cause the outer wall of the graft to press against the inner wall of the vessel, thereby providing the additional function of providing a seal, preventing fluid flow to the region between the graft and the vascular wall.
However, the use of generally cylindrical grafts to reinforce vascular walls in a patient is not without problems. Grafts are required to be compressed into a catheter before being delivered and deployed into final position. Furthermore, grafts compressed into a catheter for delivery must be capable of bending around comers and branches of the patient""s vascular system. The graft must accordingly be sufficiently flexible to satisfy these requirements.
One of the challenges encountered with the use of a flexible graft is that, because a diseased vessel is often irregularly shaped, the ends of the graft, even when urged outwardly by an attachment system, may not have a continuous circumferential edge pressed firmly against the inner wall of the vessel. As a result, fluid may leak into or out of (through a branch vessel) the region between the graft and the vascular wall, thereby increasing fluid pressure on the weakened walls of the vessel and reducing the protective effect of the graft. The same problem will occur if, as a result of an error in pre-operative sizing of the diseased vessel, a graft is provided that has a diameter slightly smaller than the diameter of the diseased vessel. Moreover, in the event the target vessel changes shape over time (i.e., increase in neck diameter or shrinkage in aneurysm), perigraft flow may occur. It will be appreciated that in these situations, because the fabric from which grafts are conventionally made is not circumferentially expandable, a complete seal around the circumference of the vessel will likely not be achieved.
Accordingly, there is a need for an improved graft that provides an enhanced seal for substantially preventing the flow of blood into the region between the graft and the vascular wall.
Briefly, and in general terms, an intraluminal graft in accordance with the present invention is structured to provide an enhanced seal between the graft and the wall of a lumen within which the graft is implanted. The graft of the present invention generally comprises a tubular member, at least one expandable attachment system connected to the tubular member, and at least one expandable sealing member connected to an exterior wall of the tubular member.
In one aspect of the invention, the graft of the present invention is adapted to be radially compressed to a reduced diameter to facilitate insertion into a patient""s vasculature and for advancement within the vasculature to a desired location. The graft is further adapted to be radially expandable from its compressed condition to an expanded condition for engagement with the vascular wall, and thus, the graft is contemplated to be made from a biocompatible material. In further embodiments, the graft may be bifurcated to have left and right branches, each with an opening at an inferior end.
The attachment system of the present invention is configured to have a generally cylindrical profile, and is adapted to be radially compressed to a reduced diameter. The attachment system is radially expandable from its compressed condition to an expanded condition, to facilitate implantation of a graft within vasculature. At least one attachment system is connected to the wall of the graft, at a superior end portion thereof. In further embodiments, additional attachment systems may be connected to the graft to provide additional attachment to the vascular wall as desired.
According to one embodiment of the present invention, a sealing member manufactured from a generally flexible fabric and having a frusto-conical shape is connected to an exterior wall of the tubular member of the graft. The sealing member is supported by a biasing member which may be formed from a generally undulating wire frame configured to provide the frusto-conical profile of the sealing member and to impart an outward bias sufficient to compress the sealing member against the vasculature. The sealing member advantageously provides the graft with the ability to expand to assume the shape of the vasculature at the target site, thereby preventing fluid flow into the region between the graft and the vascular wall.
In a second embodiment of the invention, the graft is configured with a sealing member that is adapted to cooperate with the outward expansion of an attachment system of the graft so that, upon deployment of the graft, the sealing member is moved from a first position remote from the attachment system to a second position overlapping the attachment system. In the deployed state, the sealing member of this embodiment cooperates with fluid flow to enhance the seal between tubular member and vascular wall. Additionally, tufted yarn possibly impregnated with thrombogenic material may be attached to the sealing member, thereby further enhancing the sealing effect.
In a third embodiment, the improved graft is adapted with a sealing member that has a flexible disk configuration. In this embodiment, a generally undulating biasing member provides the sealing member with an outward bias. The outward bias of the wire frame causes the sealing member to be pressed against the wall of the vessel, substantially preventing leakage between sealing member and vascular wall.
In a fourth embodiment, there is provided a disk-shaped sealing member, an outer circular edge of which is configured with a wire hoop biasing member. The wire hoop biasing member is packed into a delivery capsule by folding the hoop into a generally zig-zag shape. When deployed from the delivery capsule, the wire hoop unfolds into a circular profile to thereby substantially prevent leakage between sealing member and vascular wall.
In a fifth embodiment, the sealing member has a toroid shape, the outer surface of which is made from a flexible fabric, and the interior of which may be filled with a thrombogenic material such as polyester filaments. It is to be recognized that the seal fabric may be very thin compared to graft since the seal fabric only needs to initiate clotting. The toroid-shaped sealing member is configured to fill with the patient""s blood which will subsequently coagulate with the thrombogenic material, thereby creating a rigid obstacle to the flow of blood between sealing member and the vascular wall. In another aspect of the invention, thrombogenic filling material may be introduced into the toroid-shaped interior of the sealing member after the graft has been delivered to a desired position in the patient""s vasculature. Additionally, small apertures may be created in a wall between the graft and sealing member so that the sealing member fills with blood flowing from the interior of the graft.
In a sixth embodiment, the sealing member may be formed entirely from tufts of yarn which are fixed to the outer surface of the graft. A method of manufacturing such a graft is also disclosed.
Other features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.